1. Field of the Invention
The present invention relates to a saw blade for an electric compass- or keyhole-saw with a saw part which along a longitudinal side thereof is provided with a saw-tooth means and on which a clamping part is attached or adjoins the longitudinal side thereof. The saw blade with the clamping part is clampable between two clamping pieces of a clamping device of the compass- or keyhole-saw with a clamping or tensioning screw and the clamping part has a centering opening as well as an insert or plug opening through which the clamping or tensioning screw extends and also including two clamping or tensioning tongues equal in length and extending in the longitudinal direction of the saw blade, such tongues delimiting or defining the limits of the openings.
2. Description of the Prior Art
Saw blades of compass- or keyhole-saws are placed having the clamping part of such saw blades located between the two clamping pieces of the clamping device and the clamping part is clamped between the clamping pieces with the clamping or tensioning screw. U.S. Pat. No. 3,805,383-McNally issued Apr. 23, 1974, generically discloses a clamping part provided with the centering opening and the insert or plug opening. The clamping or tensioning screw passes through the insert or plug opening, while a centering pin of a lifting mechanism engages in the centering opening; the saw blade is moved back and forth with the lifting mechanism during operation of the compass- or keyhole-saw. The two clamping tongues, which extend in longitudinal direction of the saw blade and which laterally delimit or define the limits or boundaries of the plug or inside opening are made or constructed tapered in a direction toward a free end thereof. The outer sides thereof away from each other are rounded-off in a partially circular shape, while the inner sides thereof toward each other are straight and extend in a direction diverging toward the end of face side thereof. Consequently the two clamping tongues terminate respectively in a point, tip or apex. The plug or insert opening for the clamping or tensioning screw has only a small or nominal depth. A head of the clamping or tensioning screw taken in axial direction of the tensioning screw projects consequently over the ends or face sides of the clamping tongues. The clamping force produced by the clamping or tensioning screw via the head thereof consequently is not effective uniformly upon the clamping part, since the head as seen in a projection extends or projects over the clamping part. The clamping pieces, however, project so far over the ends or face sides of the clamping tongues that the screw head engages completely upon the one clamping piece. When consequently the clamping or tensioning screw is tightened, the clamping force produced by the screw head is transmitted or transferred only partially upon the clamping part. In a region in which the screw head taken in projection extends or projects over the clamping tongues in longitudinal direction of the saw blade, the clamping pieces in this region are clamped directly against each other. The consequence hereof is that at least the one clamping piece sets or adjusts slanted or at an incline so that a gap is formed between the one clamping piece and the saw blade at the end of the clamping device located opposite the clamping or tensioning screw. Consequently the saw blade during saw operation has a play transverse to the saw blade plane, which leads to a fluttering, pulsation or shimmying of the saw blade. A clean and accurate saw cut cannot be carried out any more as a result of this problem. Additionally, there exists the danger that the saw blade breaks or fails. Such a danger of breakage or failure of the saw blade also exists in the region of the clamping part. The cutting pressure arising during saw operation is conveyed into the clamping device, since the clamping part is supported with the longitudinal sides thereof away form each other along corresponding counter surfaces of the one clamping piece. Since the clamping tongues however extend into a point, tip or apex, the width thereof decreases considerably in a direction toward the free tongue end. The clamping tongue is strongly loaded or burdened during saw operation. As a consequence of the reduction of the cross section thereof, such clamping tongue however can only take up comparatively small or nominal forces. This clamping tongue then breaks off with higher or greater loading, stress or strain. Also the clamping part itself is then stressed or strained considerably at the transition to the saw part during saw operation or sawing. The clamping pieces extend only as far as to this transitional region so that only the clamping part, not, however, the saw part, is supported counter to the cutting pressure. The clamping part is comparatively narrow with known saw blade configuration. As a consequence of the stress or strain of the saw part arising during saw operation or sawing for this reason the saw blade tears at this transitional region from the clamping part to the saw part.
Saw blades are also known which at the clamping part have only a single clamping tongue, of which the outer side lies in the outer side of the clamping part. The clamping screw is so arranged in relation to the saw blade that the screw head, taken or seen in the projection upon the saw blade plane, overlaps the clamping tongue. Since only one clamping tongue, arranged eccentrically or off-center is provided, the saw blade is loaded even more unfavorably and disadvantageously than saw blades which have two clamping tongues.